1. Field of the Invention
The present invention relates to a recording apparatus, such as a facsimile receiver, which has a linear array of dot-forming elements, for recording images such as letters, symbols and graphical representations, in the form of dots arranged in a plurality of parallel lines, according to a batch of line data representative of lines of information to be recorded. For example, a facsimile receiver has a thermal print head having a multiplicity of heat-generating elements arranged in a straight row parallel to the lines to be recorded on a heat-sensitive paper supported on a platen. The heat-generating elements are selectively energized to record each line according to a corresponding set of line data indicative of the presence and absence of dots at predetermined recording positions equally spaced from each other along the line. Upon completion of recording of each line, the paper is fed by a suitable feeding device, by a predetermined incremental distance in the direction perpendicular to the row of the heat-generating elements. The facsimile receiver may have two different modes of recording, e.g., a standard recording mode in which a single set of line data is used to record two successive lines, and a fine or high-resolution recording mode in which each line is recorded according to the corresponding set of line data.
In the standard recording mode, therefore, the dot pattern of the first one of the two successive lines accurately represents the original image to be reproduced, but the dot pattern of the second line is identical with that of the first line, irrespective of the image in the corresponding original line. In other words, the second line of the two successive lines recorded according to a set of line data is not an accurate reproduction of the original image. In this respect, the fine or high-resolution recording mode is suitably used when the original images to be reproduced include intricate or minute patterns, or curved or inclined lines or shapes. In the standard recording mode, even these patterns of images are recorded such that two successive lines are recorded with the heat-generating elements energized according to a same set of line data. Thus, it will be understood that the resolution of the images recorded in the standard recording mode is lowered to a half of that in the high-resolution mode.
Where a curved or inclined line intersecting the direction of arrangement of the dot-forming elements is recorded in the standard recording mode, the dot in the second line of the two lines recorded according to each set of line data is located at the same position as the dot in the first line, as viewed in the direction parallel to the lines. That is, the position of the dot in the second line is offset from the actual position of the curved or inclined line, i.e., from the intersection of the original curved or inclined line and the recorded second line. Accordingly, the recorded curved or inclined line includes straight segments parallel to the feeding direction of the paper, and therefore includes stepped portions, which make it difficult for the reader to recognize the recorded image as a continuously or smoothly curved or inclined line similar to the original image. Thus, the image reproduction accuracy or resolution in the standard recording mode is considerably lower than that in the high-resolution recording mode.
On the other hand, it is noted that the size of the dots recorded on a heat-sensitive paper by heat-generating elements as the dot-forming elements is almost equal to the effective recording size of the heat-generating elements. If the effective recording size of the heat-generating elements in the feeding direction of the paper is smaller than the incremental feeding distance of the paper (i.e., line spacing), there is left a blank spacing between adjacent two lines, or between recorded dots in the adjacent two lines.
To eliminate such a blank spacing, it is proposed to increase an energy supplied to the heat-generating elements, for thereby enlarging the size of the dots recorded on the heat-sensitive paper by the energized heat-generating elements. This solution is based on the fact that the dot size increases with the amount of heat generated by the heat-generating elements.
However, the increase in the electric power applied to the heat-generating elements results in shortening the life expectancy of the heat-generating elements and therefore lowering the durability of the recording apparatus per se. Further, the increase in the amount of heat applied to the heat-sensitive paper leads to difficulty in controlling the shape of the recorded dots, namely, tendency toward rounding of the dot shape, whereby the quality of the recorded image is lowered. Moreover, the above solution requires an increased amount of power consumption for energizing the heat-generating elements, and consequently requires a relatively large power source, thereby resulting in increased size and cost of the apparatus.